In the manufacturing process for making semiconductor products such as a semiconductor integrated circuits, liquid crystal panels, solar battery panels, and magnetic disks, or flat displays or other electronic instruments, plasma is first generated within a rare gas atmosphere and then a variety of processes are performed using the plasma, such as plasma CVD, plasma oxidation, plasma nitridation, plasma oxynitridation, reactive ion etching and the like.
When introducing a substrate or the like for a semiconductor display or other electronic instrument product into the processor where these processes are performed, nitrogen is employed as the atmospheric gas, and argon, krypton or xenon, and a gas that contributes to the reaction, are introduced into the processor as gases for the plasma process. The plasma is then generated under reduced pressure using high frequency induction or microwave excitation. Afterwards, these used gases are then exhausted using a vacuum pump, rendered harmless in a detoxifying device, and released into the air. Before removing the processed substrate from the evacuated processor, the vacuum state within the processor is returned to atmospheric pressure, and nitrogen gas is introduced into the processor to prevent air from becoming mixed into the device.
Regarding the aforementioned gas that contributes to the reaction, small amounts of oxygen or small amounts of oxygen and hydrogen can be employed in the case of a plasma oxidation process; and small amounts of nitrogen and hydrogen or ammonia may be employed in the case of a plasma nitridation process. In the case of an oxynitridation process, into which investigations have begun of late, these gases may be used in combination.
In the past, argon has primarily been used as the rare gas comprising the atmospheric gas for these types of processes. In recent years however, with higher quality processing the objective, it has come to be understood that krypton and xenon, which have low-ionization potential, are extremely beneficial as gases that can form a film of superior properties. Accordingly, these gases have been coming into use.
However, krypton and xenon are only contained in air in trace amounts. Thus, in order to separate and purify krypton and xenon from the air, it is not only necessary to process a large amount of air, but the separating and purifying process becomes complicated. As a result, purified krypton and xenon are extremely expensive. Thus, in order to practically realize a process employing krypton or xenon, it is extremely important to establish a system in which the used krypton and xenon can be reclaimed, purified and reutilized in the processor.
However, the gas exhausted in these types of processors consists mainly of the rare gas and nitrogen, with trace amounts of oxygen, hydrogen, and water vapor included from the oxidation process, as well as nitrogen and hydrogen reaction products such as ammonia, ammonium ion, N—H radical, etc. included from the nitridation process. Further, nitrogen oxides are added in the oxynitridation process. Accordingly, it has been extremely technically difficult to reclaim and reutilize the rare gas, given that multiple reactive trace constituents must be removed from the exhaust gas without inviting loss of the rare gas.
A variety of processes for simply separating and purifying a specific constituent from a mixed gas of this type have been reported. For example, Japanese Patent Application, First Publication No. Sho 52-65762 discloses that use of copper oxide or copper powder and palladium powder is effective as a remover for removing oxygen or hydrogen present in a mixed gas, for example.
Japanese Patent Application, First Publication No. Hei 10-7410 discloses a method for removing water from argon by bringing argon containing oxygen into contact with a deoxygenation catalyst and hydrogen, converting the oxygen into water, and then bringing this into contact with the adsorbent zeolite.
Regarding the removal of nitrogen oxides (NOx), Japanese Patent Application, First Publication No. Hei 10-85587 discloses an NOx adsorbent which efficiently adsorbs and removes low concentrations of nitrogen oxides from a gas such as combustion gas in a highway tunnel, where a large amount of moisture and a low concentration, on the order of several ppm, of nitrogen oxides are both present.
Japanese Patent Application Hei 6-327973 discloses both a method for removing nitrous oxide (N2O) in exhaust gas, along with dust, which is one cause of the global warming effect and destruction of the ozone layer, and a filter-type removal equipment which can easily, inexpensively and effectively reduce nitrous oxide.
Japanese Patent Application 2001-120951 discloses a treatment method and device that can very efficiently adsorb nitrogen oxides, desorb the adsorbed nitrogen oxides to a high concentration, and easily crack and remove the desorbed nitrogen oxide.
However, all of the technologies disclosed in these patent applications are processes that address only one type of constituent from among nitrogen oxides, hydrogen and oxygen. These are not techniques for reclaiming a beneficial gas from a gas that is flowing at low volume and contains multiple types of trace constituents, as in the case of the gas discharged from the various processes for manufacturing a semiconductor device or other electronic instrument. In other words, these are not technologies which provide a unified arrangement for separating/removing/purifying trace constituents contained in an exhaust gas, in order to reclaim a beneficial gas from the gas discharged from the processor for manufacturing a semiconductor device or other electronic instrument.
On the other hand, Japanese Patent Application, First Publication No. 2001-232134 discloses a purifying method for the case where fluorine, krypton, nitrogen, oxygen, carbon monoxide, carbon dioxide and water are included in the neon gas removed from a KrF excimer laser oscillator in a semiconductor manufacturing device, consisting of a first step of removing fluorine; a second step of removing the oxygen using a metal oxide catalyst and then removing the carbon dioxide and water by adsorption; a third step of removing the krypton using low temperature adsorption; and a fourth step of removing the nitrogen and carbon monoxide using further low temperature adsorption. However, in this method, it is necessary to use low-temperature adsorption frequently, making a large facility for cooling necessary. Thus, this is a troublesome and costly process. While this may be a process that is suitable for employment by an industrial gas maker within its facility, it would be difficult to employ this process at a manufacturing site for semiconductor devices or electronic instruments, and, moreover, near the plasma processing facilities, as a process for sequentially separating, reclaiming and reutilizing a rare gas from the gases removed from the device.
Thus, it has been problematic that there has been no suitable process from among the various technologies known conventionally that can be used near the manufacturing equipment for semiconductor devices or other electronic instruments, and is capable of efficiently removing two or more types of constituents that are included in addition to a rare gas in the gas discharged from the various processes for manufacturing a semiconductor device or other electronic instrument. In particular, while investigations have been made of various types of removing device according to the type of constituent contained in the exhaust gas in addition to a rare gas, no process has been established that is capable of efficiently removing a plurality of constituents from a mixed gas that contains these along with a rare gas, and can limit the loss of the rare gas and thus enable a high rate of reutilization thereof.
It is thus the objective of the present invention to provide a gas purifying process and device that can remove with high efficiency and low cost such trace constituents as hydrogen, hydrogen and nitrogen reaction products, and water vapor, as well as nitrogen oxides, that are included in a mixed gas containing a rare gas, and more particularly, that can be applied to the exhaust gases from the various processes of oxidation, nitridation, and oxynitridation that use expensive krypton and xenon, and moreover, that enables realization of a small-scale system that can be disposed near the manufacturing equipment for making semiconductor devices or other electronic instruments, that is capable of continuously separating, reclaiming, and reutilizing the rare gas present in the exhaust gas.